ENJOY CHEMISTRY 1.SOME BASIC CONCEPTS OF CHEMISTRY. Some Important Points and Terms of the Chapter

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1 ENJOY CHEISTRY 1.SOE ASIC CONCEPTS OF CHEISTRY Some Important Points and Terms of the Chapter 1. Anything which has mass and occupies space is called matter. 2. atters exist in three physical states viz. solid, liquid and gas. 3. In solids, these particles are held very close to each other in an orderly fashion and there is not much freedom of movement. In liquids, the particles are close to each other but they can move around. However, in gases, the particles are far apart as compared to those present in solid or liquid states and their movement is easy and fast. 4. Solids have definite volume and definite shape. 5. Liquids have definite volume but not the definite shape. They take the shape of the container in which they are placed. 6. Gases have neither definite volume nor definite shape. They completely occupy the container in which they are placed. 7. A mixture contains two or more substances present in it (in any ratio) which are called its components. 8. A mixture may be homogeneous or heterogeneous. 9. In a homogeneous mixture, the components completely mix with each other and its composition is uniform throughout. Sugar solution and air are thus, the examples of homogeneous mixtures. 10. In heterogeneous mixtures, the composition is not uniform throughout and sometimes the different components can be observed. For example, the mixtures of salt and sugar, grains and pulses along with some dirt (often stone) pieces, are heterogeneous mixtures The components of a mixture can be separated by using physical methods such as simple hand picking, filtration, crystallization, distillation etc. 12. Pure substances have characteristics different from the mixtures. They have fixed composition, Copper, silver, gold, water, glucose are some examples of pure substances. Zonal Institute Of Education And Training; hubaneswar

2 Glucose contains carbon, hydrogen and oxygen in a fixed ratio and thus, like all other pure substances has a fixed composition. Also, the constituents of pure substances cannot be separated by simple physical methods. 13. An element consists of only one type of particles. These particles may be atoms or molecules. Sodium, copper, silver, hydrogen, oxygen etc. are some examples of elements. They all contain atoms of one type. However, the atoms of different elements are different in nature. Some elements such as sodium or copper, contain single atoms held together as their constituent particles whereas in some others, two or more atoms combine to give molecules of the element. Thus, hydrogen, nitrogen and oxygen gases consist of molecules in which two atoms combine to give their respective molecules. 14. hen two or more atoms of different elements combine, the molecule of a compound is obtained. The examples of some compounds are water, ammonia, carbon dioxide, sugar etc. the atoms of different elements are present in a compound in a fixed and definite ratio and this ratio is characteristic of a particular compound. 15. The SI system(systeme International d Unités abbreviated as SI)) has seven base units and they are listed in Table ass of a substance is the amount of matter present in it while weight is the force exerted by gravity on an object. The mass of a substance is constant whereas its weight may vary from one place to another due to change in gravity. 17. Volume has the units of (length) 3. So in SI system, volume has units of m 3. A common unit, litre (L) which is not an SI unit, is used for measurement of volume of liquids. 1 L = 1000 ml, 1000 cm 3 = 1 dm 3 Zonal Institute Of Education And Training; hubaneswar

3 18. Density of a substance is its amount of mass per unit volume SI units of density kg m 3 This unit is quite large and a chemist often expresses density in g cm There are three common scales to measuretemperature C (degree celsius), F (degree Fahrenheit) and K (Kelvin). Here, K is the SI unit. 20. The Kelvin scale is related to Celsius scale as follows :K = C The F scale is related to Celsius scale as follows 22. In scientific notation (exponential Notation) any number can be represented in the form N 10 n where n is an exponent having positive or negative values and N can vary between 1 to 10. Thus, we can write as X10 2 in scientific notation. Note that while writing it, the decimal had to be moved to the left by two places and same is the exponent (2) of 10 in the scientific notation. Similarly, can be written as 1.6 X10 4. Here the decimal has to be moved four places to the right and ( 4) is the exponent in the scientific notation. 23. Significant figures are meaningful digits which are known with certainty. The uncertainty is indicated by writing the certain digits and the last uncertain digit. Thus, if we write a result as 11.2 ml, we say the 11 is certain and 2 is uncertain and the uncertainty would be 1 in the last digit. Unless otherwise stated, an uncertainty of +1 in the last digit is always understood. 24. There are certain rules for determining the number of significant figures. These are stated below: a) All non-zero digits are significant. For example in 285 cm, there are three significant figures and in 0.25 ml, there are two significant figures. b) Zeros preceding to first non-zero digit are not significant. Such zero indicates the position of decimal point. Thus, 0.03 has one significant figure and has two significant figures. c) Zeros between two non-zero digits are significant. Thus, has four significant figures. d) Zeros at the end or right of a number are significant provided they are on the right side of the decimal point. For example, g has three significant figures. ut, if otherwise, the terminal zeros are not significant if there is no decimal point. For example, 100 has only one significant figure, but 100. has three significant figures and has four significant Zonal Institute Of Education And Training; hubaneswar

4 figures. Such numbers are better represented in scientific notation. e can express the number 100 as for one significant figure, for two significant figures and for three significant figures. e) Counting numbers of objects, for example, 2 balls or 20 eggs, have infinite significant figures as these are exact numbers and can be represented by writing infinite number of zeros after placing a decimal i.e.,2 = or 20 = f) In numbers written in scientific notation, all digits are significant e.g., has three significant figures, and has four significant figures. 25..Law of Conservation of ass states that matter can neither be created nor destroyed. 26. Law of Definite Proportions states that a given compound always contains exactly the same proportion of elements by weight. 27. Law of ultiple Proportions states that if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers. 28. Gay Lussac s Law of Gaseous Volumes: This law was given by Gay Lussac in He observed that when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at same temperature and pressure. 29. In 1811, Avogadro proposed that equal volumes of gases at the same temperature and pressure should contain equal number of molecules. 30. In 1808, Dalton published A New System of Chemical Philosophy in which he proposed the following : a) atter consists of indivisible atoms. b) All the atoms of a given element have identical properties including identical mass. Atoms of different elements differ in mass. c) Compounds are formed when atoms of different elements combine in a fixed ratio. d) Chemical reactions involve reorganization of atoms. These are neither created nor destroyed in a chemical reaction. e) Dalton s theory could explain the laws of chemical combination. 31. One atomic mass unit is defined as a mass exactly equal to one twelfth the mass of one carbon - 12 atom. Zonal Institute Of Education And Training; hubaneswar

5 32. olecular mass is the sum of atomic masses of the elements present in a molecule. It is obtained by multiplying the atomic mass of each element by the number of its atoms and adding them together. 33. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in kilogram of carbon-12; its symbol is mol. hen the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. This number of entities in 1 mol is so important that it is given a separate name and symbol. It is known as Avogadro constant, denoted by N A in honor of Amedeo Avogadro. 34. An empirical formula represents the simplest whole number ratio of various atoms present in a compound whereas the molecular formula shows the exact number of different types of atoms present in a molecule of a compound. 35. any a time, the reactions are carried out when the reactants are not present in the amounts as required by a balanced chemical reaction. In such situations, one reactant is in excess over the other. The reactant which is present in the lesser amount gets consumed after sometime and after that no further reaction takes place whatever be the amount of the other reactant present. Hence, the reactant which gets consumed, limits the amount of product formed and is, therefore, called the limiting reagent. 36. ass per cent = ass of solute per 100 g of solution ass of solute = 100 ass of solution It is the amount of solute in grams dissolved per 100 g of solution. e.g., 10% solution of sodium chloride means 10 g of solid sodium chloride present in 100 g of solution. 37. ole Fraction: It is ratio of number of moles of a particular component to the total number of moles of all the components. No.of moles of solute ole-fraction of solute = No.of moles of solute No.of moles of solvent Zonal Institute Of Education And Training; hubaneswar

6 x n A n n A A x in case of dilute solution A A < < A A 38. olality (m). It is defined as number of moles of solute () per 1000 g or 1 kg of solvent. olality () = No. of moles of solute solvent Kg. of A 1000 in grams. where A is mass of solvent. 39. olarity (). It is expressed as the number of moles of solute per litre of solution. olarity () = No. of moles of solute Litres of solution Volume 1000 of solution in ml.. where is mass of solute, is molar mass of solute

7 Unit-1 SOE ASIC CONCEPTS OF CHEISTRY 1. Question based on significant numbers,precision,accuracy, ScientificNotation, laws of chemical combinations, SI units 1.1 hat are the SI unit of mass, length & time? 1.2 atch the following prefixes with their multiples: Prefixes ultiples (i) micro 10 6 (ii) deca 10 9 (iii)mega 10 6 (iv) giga (v)femto 10 (vi) pico (a) hat do you mean by significant figures? hat are rules for determining the number of significant figures? (b)explain the terms: Precision and Accuracy 1.4 Express the following in the scientific notation: (i) (ii) 234,000 (iii) 8008 (iv) (v) How many significant figures are present in the following? (i) (ii) 208 (iii) 5005 (iv) 126,000 (v) (vi) Round up the following upto three significant figures: (i) (ii) (iii) (iv) The following data are obtained when dinitrogen and dioxygen react together to form different compounds : S.No ass of ass of dinitrogen dioxygen 1 14 g 16 g Zonal Institute Of Education And Training; hubaneswar

8 2 14 g 32 g 3 28 g 32 g 4 28 g 80 g (a) hich law of chemical combination is obeyed by the above experimental data? Give its statement. 1.8 Convert the following into basic units: (i) 28.7 pm (ii) pm (iii) mg 1.9 How many significant figures should be present in the answer of the following calculations? State and illustrate the law of constant proportions State and explain the law of multiple proportions. 2. Question based on atomic and molecular masses Atomic ass Average Atomic ass, olecular ass, Formula ass, mole concept and molar asses, percentage composition, Empirical Formula for olecular Formula, Limiting Reagent. 2.1 Calculate the molecular mass of the following: (i) H 2 O (ii) CO 2 (iii) CH 4 (iv) C 6 H 12 O Calculate the mass per cent of different elements present in sodium sulphate (Na 2 SO 4 ). 2.3 Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% Dioxygen by mass. 2.4 How much copper can be obtained from 100 g of copper sulphate (CuSO 4 )? 2.5 In a reaction A Identify the limiting reagent, if any, in the following reaction mixtures. (i) 300 atoms of A molecules of (ii) 2 mol A + 3 mol (iii) 100 atoms of A molecules of (iv) 5 mol A mol (v) 2.5 mol A + 5 mol 2.5 Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen are 69.9 and 30.1 respectively. 2.6 Calculate the atomic mass (average) of chlorine using the following data: Isotope % Natural olar ass Abundance 35 Cl Cl In three moles of ethane (C 2 H 6 ), calculate the following: (i) Number of moles of carbon atoms. (ii) Number of moles of hydrogen atoms. (iii) Number of molecules of ethane. 2.8 If ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced? Zonal Institute Of Education And Training; hubaneswar

9 2.9A welding fuel gas contains carbon and hydrogen only. urning a small sample of it in oxygen gives 3.38 g carbon dioxide, g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate (i) empirical formula, (ii) molar mass of the gas, and (iii) molecular formula Calculate the amount of water (g) produced by the combustion of 16 g of methane. reaction How many moles of methane are required to produce 22 g CO 2 (g) after combustion? 2.12 A compound contains 4.07 % hydrogen,24.27 % carbon and % chlorine. Its molar mass is g. hat are its empirical and molecular formulas? 3. Question based on ass per cent, olarity, ole fraction, olality 3.1(i) Define the following terms. (rite the mathematical formulas related to terms)(a) ass percent (b) olarity (c) olality (d) ole-fraction (e) ass percent (ii)calculate the mass of sodium acetate (CH 3 COONa) required to make 500 ml of molar aqueous solution. (olar mass of sodium acetate is g mol 1 ). 3.2 Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g ml 1 and the mass per cent of nitric acid in it being 69%. 3.3 hat is the concentration of sugar (C 12 H 22 O 11 ) in mol L 1 if its 20 g are dissolved in enough water to make a final volume up to 2L? 3.4 If the density of methanol is kg L 1, what is its volume needed for making 2.5 L of its 0.25 solution? 3.5 A sample of drinking water was found to be severely contaminated with chloroform, CHCl 3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass). (i) Express this in percent by mass. (ii) Determine the molality of chloroform in the water sample. 3.6 The density of 3 solution of NaCl is 1.25 g ml 1. Calculate molality of the solution. 3.7 How are 0.50 mol Na 2 CO 3 and 0.50 Na 2 CO 3 different? 3.8 hich one of the following will have largest number of atoms? (i) 1 g Au (s) (ii) 1 g Na (s) (iii) 1 g Li (s)(iv) 1 g of Cl 2 (g) 3.9 Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is (assume the density of water to be one) Calculate the number of atoms in each of the following (i) 52 moles of Ar (ii) 52 u of He (iii) 52 g of He. 3.11Calculate the molarity of NaOH in the solution prepared by dissolving its 4 g in enough water to form 250 ml of the solution. Zonal Institute Of Education And Training; hubaneswar

10 3.12 A solution is prepared by adding 2 g of a substance A to 18 g of water. Calculate the mass per cent of the solute How does molality & olarity depend on temperature? Out of molality & olarity which one is better way to express concentration? ANSERS 2.1 Calculate the molecular mass of the following: Ans: (i) H 2 O = 18 (ii) CO 2 =44 (iii) CH 4 =16 (iv) C 6 H 12 O 6 = Calculate the mass per cent of different elements present in sodium sulphate (Na 2 SO 4 ). Ans % Na= 46 X100/142=32.4, %S= 32 X100/142= 22.53, %O = 64X100/142= Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% Dioxygen by mass. Ans: no of moles of Fe: 69.9/56= no of moles of O =30.1/ 16= whole number ratio between the number of moles = 1: 1.5= 2: 3. Hence empirical formula is Fe 2 O How much copper can be obtained from 100 g of copper sulphate (CuSO 4 )? Ans: 63.5g of Cu in 159.5g of CuSO X100/159.5g = 39.81g of Cu in 100g of CuSO In a reaction A Identify the limiting reagent, if any, in the following reaction mixtures. (i) 300 atoms of A molecules of Ans: is limiting (ii) 2 mol A + 3 mol Ans: A is limiting (iii) 100 atoms of A molecules of Ans: reactants totally consumed (iv) 5 mol A mol Ans: is limiting (v) 2.5 mol A + 5 mol Ans: A is limiting Zonal Institute Of Education And Training; hubaneswar

11 2.6 Calculate the atomic mass (average) of chlorine using the following data: Isotope % Natural olar ass Abundance 35 Cl Cl Ans: ( X75.77) + ( X24.23)/100 = In three moles of ethane (C 2 H 6 ), calculate the following: (i) Number of moles of carbon atoms. Ans: 3X2= 6 (ii) Number of moles of hydrogen atoms. Ans: 3X6= 18 (iii) Number of molecules of ethane. Ans: 3X 6.023X10 23 =18.069X If ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced? Ans: 2H 2(g) + O 2(g) 2H 2 O (g); 10 volumes of water vapour 2.9A welding fuel gas contains carbon and hydrogen only. urning a small sample of it in oxygen gives 3.38 g carbon dioxide, g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate (i) empirical formula, (ii) molar mass of the gas, and (iii) molecular formula. Ans: i. 12g of C in 44g of CO 2 =>(12/44)X3.38g of C in 3.38g of CO 2 = ii. 2g of H in 18g of H 2 O => (2/18) X of H in 0.690g of H 2 O=0.077 No of oles of C= 0.922/12= No of moles of H =0.077 The empirical formula =CH 22.4L at STP =1 molar mass 10L at STP weighs11.6g; 22.4L will weigh (11.6/10)X22.4= 26 iii. Empirical formula mass= 13 olecular mass=26 The ratio of molecular mass: empirical formula mass=2 Hence molecular formula is C 2 H 2 Zonal Institute Of Education And Training; hubaneswar

12 2.10 Calculate the amount of water (g) produced by the combustion of 16 g of methane. Ans: CH 4 + 2O 2 2H 2 O + CO 2; 16g CH 4 is 1mole. From the stoichiometric equation we get 1mole of methane gives 2moles of H 2 O. ie is 18X2 =36g of water How many moles of methane are required to produce 22 g CO 2 (g) after combustion? Ans: 22g of CO 2 is 22/44 moles ie 0.5 moles; 1mole of CH 4 produces 1mole of CO 2. Hence 0.5 moles of methane is required A compound contains 4.07 % hydrogen,24.27 % carbon and % chlorine. Its molar mass is g. hat are its empirical and molecular formulas? Ans: no of moles of H =4.07; C=24.27/12= 2.02; 71.65/35.5= 2.02 Simplest whole number ratio H: C:O= 2:1:1 Hence empirical formula is CH 2 O 3. Question based on ass per cent, olarity, ole fraction, olality 3.1 (ii)calculate the mass of sodium acetate (CH 3 COONa) required to make 500 ml of molar aqueous solution. (olar mass of sodium acetate is g mol 1 ). Ans: no of moles of sodium acetate (CH 3 COONa) required = (0.375/1000) X500=0.1875,ie X g = 15.38g 3.2 Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g ml 1 and the mass per cent of nitric acid in it being 69%. Ans: 69g of HNO 3 in 100g of sample. => 69/63=1.095moles in 100g of sample. => moles in 100/1.41ml of acid i.e 70.92ml. No of moles of HNO 3 in 1000ml= (1.095/70.92)X1000= hat is the concentration of sugar (C 12 H 22 O 11 ) in mol L 1 if its 20 g are dissolved in enough water to make a final volume up to 2L? Ans: 20g in 2lit 10g in 1 lit; 10/342= moles /lit 3.4 If the density of methanol is kg L 1, what is its volume needed for making 2.5 L of its 0.25 solution? Zonal Institute Of Education And Training; hubaneswar

13 Ans: moles of methanol required to prepare 2.5L of 0.25 methanol solution =2.5X0.25= X32g=20g of methanol. 793g of methanol is present in 1000ml. => 20g is present in (1000/793) X 20 ml of methanol sample ml of methanol is used to prepare 2.5lit of 0.25 methanol. 3.5 A sample of drinking water was found to be severely contaminated with chloroform, CHCl 3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass). (i) Express this in percent by mass. Ans: (15/10 6 )X 100= 15X10-4 % by mass (ii) Determine the molality of chloroform in the water sample. Ans: ass of solute in 1kg of solvent is15x10-3 g. => 15X10-3 /119.5 = 1.26X 10-4 molal. 3.6 The density of 3 solution of NaCl is 1.25 g ml 1. Calculate molality of the solution. Ans: 1.25g/ml 1250g/lit. ass of 1 litre solution is 1250g of which 3X58.5g= 175.5g is solute. ass of solvent = = g. 3moles of solute in 1.074kg of solvent 3/1.074 moles in 1kg of solvent. Hence molality=2.79moles/kg 3.8 hich one of the following will have largest number of atoms? (i) 1 g Au (s) (ii) 1 g Na (s) (iii) 1 g Li (s)(iv) 1 g of Cl 2 (g) Ans: iii) 1 g Li, because it has the least atomic mass among the given ones. 3.9 Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is (assume the density of water to be one). Ans: we have to calculate no of moles per litre. Let no of moles of ethanol be X. let 1 litre of water = 1kg of water. Then: X/(X )= 0.04 ;let X << then X/55.56=0.04 ; X = 2.22, Hence molarity is 2.22moles /lit 3.10 Calculate the number of atoms in each of the following (i) 52 moles of Ar; Ans: 52 X 6.022X10 23 = X =3.13 X atoms (ii) 52 u of He; Ans: 52/4= 13 atoms (iii) 52 g of He; Ans: (52/4) X 6.022X10 23 = X atoms of He. Zonal Institute Of Education And Training; hubaneswar

14 3.11Calculate the molarity of NaOH in the solution prepared by dissolving its 4 g in enough water to form 250 ml of the solution. Ans: 4g in 250ml 16g in 1 lit. 16/40moles/lit= 0.4moles /lit= A solution is prepared by adding 2 g of a substance A to 18 g of water. Calculate the mass per cent of the solute. Ans: (2/18) X 100 is the mass percent. Zonal Institute Of Education And Training; hubaneswar

Unit-1 SOME BASIC CONCEPTS OF CHEMISTRY

Unit-1 SOME BASIC CONCEPTS OF CHEMISTRY 1. Question based on significant numbers,precision,accuracy, ScientificNotation, laws of chemical combinations, SI units 1.1 What are the SI unit of mass, length